The proposed studies are unified by their common aim of elucidating general principles of cellular interactions and control systems in lower vertebrates and invertebrates. Five individual projects are included which share common approaches and methodologies: I) Neuron-glia interactions in amphibia; II) Excitation and contractile activation in crustacea; III) Synapse development in cockroach; IV) Neuron outgrowth in amphibia; and V) Neural control of sea-urchin spines. Three of the projects are also concerned with understanding principles of nervous system regeneration, an emerging theme of the program. All these studies will provide insight into more complex nervous systems and eventually lead to a rational basis for the diagnosis and treatment of a variety of neurological diseases. Furthermore, we seek support for general core facilities that are necessary for the project research: A) External communication; B) Animal collection and care; and C) Histology. These studies constitute the major research effort at the institute of Neurobiology of the Medical Sciences Campus of the University of Puerto Rico. This is an interdisciplinary, interdepartmental research facility devoted to the study of the structure and function of the nervous system, with an emphasis on comparative cellular studies. It offers investigators and students from Puerto Rico, the rest of the United States and the Americas, as well as Europe, access to the rich Caribbean marine, terrestrial and fresh water fauna for neurobiological investigations. The Institute of Neurobiology serves as a focus for bringing together researchers who are interested in various aspects of contemporary neuroscience. The number of active researchers in this field in Puerto Rico has been quite small; building on the foundation provided by this Program Project Grant, in the previous granting period the number of researchers has more than doubled and the research base has significantly broadened. In this enriched research environment productive collaborations are taking place.